Method and apparatus for determining when a fastener is tightened to a predetermined tightness by a pulse output tightening tool, and a pulsed output tightening tool incorporating the apparatus

ABSTRACT

An impact wrench ( 1 ) comprising an output shaft ( 5 ) for receiving a socket or other fastener engaging element for tightening a fastener is powered by a pneumatic motor ( 11 ). Apparatus ( 20 ) for determining when the fastener has been tightened to a predetermined tightness comprises a body member ( 21 ) extending around the output shaft ( 5 ), and an eccentrically disposed member ( 24 ) on the output shaft ( 5 ) located within a central bore ( 30 ) of the body member ( 21 ). A pair of photo sensors ( 33   a   , 33   b ) in light accommodating bores ( 34   a   , 34   b ) receive light through the bores ( 34   a   , 34   b ) from corresponding light emitting diodes ( 36   a   , 36   b ). The eccentrically disposed member ( 24 ) is located in the central bore ( 30 ) relative to the light accommodating bores ( 34   a   , 34   b ), so that as the output shaft ( 5 ) rotates, the eccentrically disposed member ( 24 ) extends into the bores ( 34   a   , 34   b ) and alternates between a position where the bores ( 34 ) are almost completely occluded to a position where almost no occlusion of the bores ( 34 ) takes place, thereby varying the light intensity received by the photo sensors ( 33 ) from minimum light intensity to maximum light intensity. A monitoring circuit ( 42 ) reads the outputs from the photo sensors ( 33 ) for determining when the fastener is tightened to its snug point, and for determining when the fastener is tightened to the predetermined tightness by reading the outputs from the photo sensors ( 33 ) for determining when the output shaft ( 5 ) has been rotated through a predetermined angular displacement from the snug point corresponding to the predetermined tightness.

The present invention relates to apparatus for use in a pulsed outputtightening tool for determining when a fastener being tightened by thetool is tightened to a predetermined tightness. The invention alsorelates to a pulsed output tightening tool, and in particular, thoughnot limited to an impact wrench incorporating the apparatus, and theinvention also relates to a method for determining when a fastener istightened to a predetermined degree of tightness by a pulsed outputtightening tool.

Pulsed output tightening tools are known. One such tool is typicallyreferred to as an impact wrench which in general, is pneumaticallypowered. Typically, impact wrenches comprise a housing within which anoutput shaft is rotatably mounted. An anvil member is located at one endof the output shaft, and a hammer mechanism located within the housingco-operates with the anvil for intermittently imparting high energyimpacts to the anvil for in turn imparting corresponding pulsedtightening moments on the output shaft for tightening a fastener. Theoutput shaft typically terminates in a receiver of square section forreceiving a socket or other fastener engaging element for engaging thefastener for tightening thereof. The hammer mechanism typically isoperated by a motor, a drive shaft of which carries the hammer mechanismso that typically on each 180° or 360° of angular rotation of the driveshaft the hammer mechanism impacts on the anvil. While in general impactwrenches are pneumatically powered, they may also be powered by anhydraulic or an electrically powered motor. In general, impact wrenchescontinuously rotate the fastener until resistance to tightening isencountered, at which stage continuous rotating of the fastener ceasesand further rotation of the fastener is achieved by the intermittentpulsed tightening moments which are imparted to the output shaft by theintermittent impacting of the hammer mechanism with the anvil.

In general, when continuous rotation of the fastener ceases, thefastener, in general, is said to be tightened to or towards its snugpoint, in other words, the point at which the parts of a joint beingsecured by the fastener become clamped and the linear tightening of thefastener has begun. It is important to determine when a fastener istightened to a desired predetermined tightness. In continuously runningtightening tools it is normal to control the torque to which thefastener is tightened. This is achieved by monitoring the tighteningtorque to which the fastener is being subjected, and on the tighteningtorque reaching a predetermined value, the fastener is deemed to havebeen tightened to the desired predetermined tightness. However,monitoring the torque to which a fastener is tightened by an impact toolproves considerably more difficult than monitoring the torque in acontinuously running tightening tool, since a direct reading of torqueis unavailable.

Various alternative techniques for determining when a fastener has beentightened to a desired predetermined tightness by an impact tool havebeen used. One such technique requires that the fastener be tightened toits snug point, and then be tightened through a predetermined angle fromthe snug point. This technique requires physically and manuallymeasuring the angle through which the fastener is tightened from thesnug point. Another technique requires that the fastener be tightened toits yield point. However, in general, these techniques suffer fromvarious disadvantages, in particular, the level of accuracy isrelatively low, and can be variable, and in many cases special tuningand calibration of the tool before each use is required.

U.S. Patent Specification No. 4,316,512 of Kibblewhite, et al disclosesan impact wrench which incorporates a control system for determiningwhen a fastener has been tightened to a predetermined tightness. In theimpact wrench of Kibblewhite the fastener is tightened to its yieldpoint. Kibblewhite's impact wrench comprises a rotary encoder which isattached to the output shaft for determining the angular displacement ofthe output shaft. In order to determine when the fastener has beentightened to the yield point, Kibblewhite monitors the angulardisplacement of the output shaft and time. By measuring the time over afixed rotational angle as a parameter representative of torque, and thenapplying gradient comparison techniques, Kibblewhite determines theyield point. While the impact wrench of Kibblewhite is suitable fortightening a fastener to its yield point, it is incapable of tighteninga fastener to any other predetermined tightness with any degree ofaccuracy. Incremental rotary encoders of the type disclosed in theKibblewhite impact wrench, with the robustness required in an impactwrench by their nature tend to give poor angular resolution. Indeed, theincremental rotary encoder of Kibblewhite has a resolution ofapproximately 5°. This is insufficient for determining with practicalaccuracy when a fastener has been tightened to its snug point, and isalso incapable of accurately detecting the angular displacement of thefastener resulting from each pulsed tightening moment. Accordingly, theimpact wrench of Kibblewhite takes no account of the snug point of thefastener, and thus, does not provide an adequate level of accuracy indetermining when a fastener has been tightened to a predeterminedtightness other than the yield point.

There is therefore a need for an apparatus for use in a pulsed outputtightening tool which overcomes the problems of prior art devices, fordetermining when a fastener is tightened to a predetermined tightness,and there is also a need for a method for determining when a fastenerhas been tightened by a pulsed output tightening tool to a predeterminedtightness. There is also a need for a pulsed output tightening tool fortightening a fastener to a predetermined tightness.

The present invention is directed towards providing such an apparatus, amethod and a pulsed output tightening tool.

According to the invention there is provided apparatus for use in apulsed output tightening tool for determining when a fastener beingtightened by a rotatable output means of the tool is tightened to apredetermined tightness, the apparatus comprising a detectable means formounting on the rotatable output means of the tool and being rotatabletherewith for providing a varying detectable characteristic as theoutput means rotates about its rotational axis, and a monitoring meansfor monitoring the detectable means for determining rotational angulardisplacement of the output means, wherein a means is providedco-operable with the monitoring means for determining when the fasteneris tightened to its snug point, and for determining when the fastener istightened to the predetermined tightness in response to the angulardisplacement of the rotatable output means from its positioncorresponding to the snug point of the fastener.

In one embodiment of the invention the means for determining when thefastener is tightened to its snug point is responsive to the monitoringmeans detecting the angular displacement of the output means being lessthan a first reference predetermined angular displacement in response toone pulsed output of the output means.

In another embodiment of the invention the means for determining whenthe fastener is tightened to the predetermined tightness is responsiveto the monitoring means determining that the rotatable output means hasrotated a second reference predetermined angular displacement from itssnug point position.

In a further embodiment of the invention the means for determining whenthe fastener is tightened to its snug point is responsive to themonitoring means detecting the first stalling of the output means aftertightening of the fastener commences.

Preferably, the detectable characteristic provided by the detectablemeans alternately and smoothly cycles between a minimum value of thedetectable characteristic and a maximum value of the detectablecharacteristic as the output means rotates for facilitating adetermination of the angular displacement of the output means inresponse to each pulsed output of the output means.

In one embodiment of the invention the detectable characteristic of thedetectable means cycles through each of the minimum and maximum valuesof the detectable characteristic at least once for each 360° angulardisplacement of the output means.

In another embodiment of the invention the detectable characteristicprovided by the detectable means varies between the minimum value andthe maximum value for each 180° of angular displacement of the outputmeans.

In a further embodiment of the invention the monitoring means outputs asignal indicative of the angular displacement of the output means.Preferably, the monitoring means outputs an electronic signal.Advantageously, the monitoring means co-operates with the detectablemeans for detecting the absolute angular position of the output means.

In one embodiment of the invention the detectable means comprises aneccentrically disposed member eccentrically disposed relative to theoutput means. Preferably, the eccentrically disposed member defines aneccentric surface, eccentrically disposed relative to the output means.Advantageously, the eccentrically disposed member defines a centralaxis, and is adapted for mounting on the output means with the centralaxis of the eccentrically disposed member spaced apart from and parallelto the rotational axis of the output means for causing the eccentricallydisposed member to rotate eccentrically with the output means. Ideally,the eccentric surface defined by the eccentrically disposed member is acylindrical surface.

In one embodiment of the invention the monitoring means is a lightsensing means. Preferably, the light sensing means co-operates with thedetectable means so that light passing the detectable means to the lightsensing means is at least partially occluded by the detectable means asthe output means rotates, and the degree of occlusion alternates betweenminimum and maximum values corresponding to the minimum and maximumvalues of the detectable characteristic. Advantageously, a body memberis provided adjacent the detectable means, and a light accommodatingbore extends through the body member for directing light onto the lightsensing means, an opening being provided into the light accommodatingbore for accommodating the detectable means into the light accommodatingbore as the output means rotates so that the light accommodating bore isat least partly occluded by the detectable means as the output meansrotates, the degree of occlusion alternating between the respectiveminimum and maximum values thereof as the output means rotates.

In one embodiment of the invention at maximum occlusion the detectablemeans substantially occludes the light accommodating bore, and atminimum occlusion the detectable means just slightly occludes the lightaccommodating bore.

In one embodiment of the invention a light source is provided at one endof the light accommodating bore and the light sensing means is providedat the other end thereof, the opening for accommodating the detectablemeans into the light accommodating bore being located intermediate theends thereof. Preferably, the light sensing means is a photo sensor.

Advantageously, a pair of monitoring means is provided, the respectivemonitoring means being angularly spaced apart around the detectablemeans for facilitating determining of the absolute angular position ofthe output means. Preferably, the respective monitoring means aredisposed at 90° to each other around the detectable means.

In one embodiment of the invention the apparatus comprises a calibratingmeans for calibrating the apparatus. Preferably, the calibrating meansis operable for calibrating the apparatus when the output means isrotating at a substantially constant speed.

Additionally the invention provides apparatus for use in a pulsed outputtightening tool for determining when a fastener being tightened by arotatable output means of the tool is tightened to a predeterminedtightness, the apparatus comprising a detectable means for mounting onthe rotatable output means of the tool and being rotatable therewith forproviding a varying detectable characteristic as the output meansrotates about its rotational axis, and a monitoring means for monitoringthe detectable means for determining rotational angular displacement ofthe output means, wherein the detectable characteristic provided by thedetectable means alternately and smoothly cycles between a minimum valueof the detectable characteristic and a maximum value of the detectablecharacteristic as the output means rotates for facilitating adetermination of the angular displacement of the output means inresponse to each pulsed output of the output means for determining whenthe fastener is tightened to the predetermined tightness.

In one embodiment of the invention the detectable characteristic of thedetectable means cycles through each of the minimum and maximum valuesof the detectable characteristic at least once for each 360° angulardisplacement of the output means.

In another embodiment of the invention the detectable characteristicprovided by the detectable means varies between the minimum value andthe maximum value for each 180° of angular displacement of the outputmeans.

In a further embodiment of the invention the monitoring means outputs asignal indicative of the angular displacement of the output means.

Preferably, the monitoring means outputs an electronic signal.

Advantageously, the monitoring means co-operates with the detectablemeans for detecting the absolute angular position of the output means.

In one embodiment of the invention a means is provided for determiningwhen the fastener is tightened to its snug point.

In one embodiment of the invention the means for determining when thefastener is tightened to its snug point is responsive to the monitoringmeans detecting the first stalling of the output means after tighteningof the fastener commences.

In another embodiment of the invention the means for determining whenthe fastener is tightened to its snug point is responsive to themonitoring means detecting the angular displacement of the output meansbeing less than a first reference predetermined angular displacement inresponse to one pulsed output of the output means.

In a further embodiment of the invention the monitoring means comprisesa computing means for computing the angular displacement of the outputmeans after the fastener is tightened to its snug point for determiningwhen the fastener is tightened to the predetermined tightness.

Preferably, the detectable means comprises an eccentrically disposedmember eccentrically disposed relative to the output means.Advantageously, the eccentrically disposed member defines an eccentricsurface, eccentrically disposed relative to the output means. Ideally,the eccentrically disposed member defines a central axis, and is adaptedfor mounting on the output means with the central axis of theeccentrically disposed member spaced apart from and parallel to therotational axis of the output means for causing the eccentricallydisposed member to rotate eccentrically with the output means.

Preferably, the eccentric surface defined by the eccentrically disposedmember is a cylindrical surface.

In one embodiment of the invention the monitoring means is a lightsensing means.

In another embodiment of the invention the light sensing meansco-operates with the detectable means so that light passing thedetectable means to the light sensing means is at least partiallyoccluded by the detectable means as the output means rotates, and thedegree of occlusion alternates between minimum and maximum valuescorresponding to the minimum and maximum values of the detectablecharacteristic.

In a further embodiment of the invention a body member is providedadjacent the detectable means, and a light accommodating bore extendsthrough the body member for directing light onto the light sensingmeans, an opening being provided into the light accommodating bore foraccommodating the detectable means into the light accommodating bore asthe output means rotates so that the light accommodating bore is atleast partly occluded by the detectable means as the output meansrotates, the degree of occlusion alternating between the respectiveminimum and maximum values thereof as the output means rotates.

Preferably, at maximum occlusion the detectable means substantiallyoccludes the light accommodating bore, and advantageously, at minimumocclusion the detectable means just slightly occludes the lightaccommodating bore.

In one embodiment of the invention a light source is provided at one endof the light accommodating bore and the light sensing means is providedat the other end thereof, the opening for accommodating the detectablemeans into the light accommodating bore being located intermediate theends thereof.

In another embodiment of the invention the light sensing means is aphoto sensor.

In a further embodiment of the invention a pair of monitoring means isprovided, the respective monitoring means being angularly spaced apartaround the detectable means for facilitating determining of the absoluteangular position of the output means.

Ideally, the respective monitoring means are disposed at 90° to eachother around the detectable means.

Further the invention provides a pulsed output tightening toolcomprising an output means rotatably mounted about a rotational axis forintermittently imparting a pulsed tightening moment to a fastener fortightening thereof, and apparatus for determining when a fastener beingtightened by the tool is tightened to a predetermined tightness, whereinthe apparatus for determining when the fastener is tightened to thepredetermined tightness comprises the apparatus according to theinvention.

The invention also provides a pulsed output tightening tool comprising arotatable output means rotatably mounted about a rotational axis forintermittently imparting a pulsed tightening moment to a fastener fortightening thereof, a detectable means being mounted on the output meansand being rotatable therewith for providing a varying detectablecharacteristic as the output means rotates, and a monitoring means formonitoring the detectable means for determining rotational angulardisplacement of the output means wherein a means is provided co-operablewith the monitoring means for determining when the fastener is tightenedto its snug point, and for determining when the fastener is tightened tothe predetermined tightness in response to the angular displacement ofthe rotatable output means from its position corresponding to the snugpoint of the fastener.

In one embodiment of the invention the output means comprises an outputshaft defining the cylindrical surface adjacent the detectable means.

In another embodiment of the invention the pulsed output tightening toolis an impact wrench, and the output shaft extends from an anvil.

In a further embodiment of the invention a hammer mechanism is providedfor co-operating with the anvil for intermittently impacting with theanvil for providing the respective pulsed tightening moments.

In one embodiment of the invention a drive means is provided foroperating the hammer mechanism for intermittently impacting with theanvil.

In another embodiment of the invention the drive means comprises a drivemotor.

In a further embodiment of the invention the drive means comprises apneumatic motor.

In one embodiment of the invention a pneumatic turbine electricalgenerator is located adjacent an exhaust from the pneumatic motor forrecovering power from the exhaust of the pneumatic motor for generatingelectricity for powering the monitoring means.

In a further embodiment of the invention a cut-out means is provided forisolating the drive means from a power source.

In a still further embodiment of the invention the cut-out means isresponsive to the monitoring means determining that the fastener hasbeen tightened to the predetermined tightness.

In another embodiment of the invention a radio receiving circuit isprovided, and the radio receiving circuit is responsive to a controlsignal received from a transmitter for operating the cut-out means forisolating power to the drive means.

In a further embodiment of the invention the transmitter is responsiveto the monitoring means determining that the fastener has been tightenedto the predetermined tightness.

The invention also provides a pulsed output tightening tool comprisingan output means rotatably mounted about a rotational axis forintermittently imparting a pulsed tightening moment to a fastener fortightening thereof, a detectable means being mounted on the output meansand being rotatable therewith for providing a varying detectablecharacteristic as the output means rotates, and a monitoring means formonitoring the detectable means for determining rotational angulardisplacement of the output means wherein the detectable characteristicprovided by the detectable means alternately and smoothly cycles betweena minimum value of the detectable characteristic and a maximum value ofthe detectable characteristic as the output means rotates forfacilitating a determination of the angular displacement of the outputmeans in response to each pulsed output of the output means fordetermining when the fastener is tightened to the predeterminedtightness.

In one embodiment of the invention the detectable characteristic of thedetectable means cycles through each of the minimum and maximum valuesof the detectable characteristic at least once for each 360° angulardisplacement of the output means.

In another embodiment of the invention the detectable characteristicprovided by the detectable means varies between the minimum value andthe maximum value for each 180° of angular displacement of the outputmeans.

In a further embodiment of the invention the monitoring means outputs asignal indicative of the angular displacement of the output means.

Preferably, the monitoring means outputs an electronic signal.

Advantageously, the monitoring means co-operates with the detectablemeans for detecting the absolute angular position of the output means.

In another embodiment of the invention a means is provided fordetermining when the fastener is tightened to its snug point.

In a further embodiment of the invention the means for determining whenthe fastener is tightened to its snug point is responsive to themonitoring means detecting the first stalling of the output means aftertightening of the fastener commences.

In a still further embodiment of the invention the means for determiningwhen the fastener is tightened to its snug point is responsive to themonitoring means detecting the angular displacement of the output meansin response to a pulsed output being less than a predetermined angulardisplacement.

Further the invention provides a method for determining when a fasteneris tightened to a predetermined tightness by a rotatable output means ofa pulsed output tightening tool, wherein the method comprises the stepsof determining when the fastener is tightened to its snug point, andmonitoring the rotational angular displacement of the output means fromits position corresponding to the snug point of the fastener until theoutput means rotates through a second reference predetermined angulardisplacement from its snug point position corresponding to thepredetermined tightness. In one embodiment of the invention the fasteneris determined as having been tightened to its snug point in response todetecting the first stalling of rotation of the output means aftertightening of the fastener has commenced.

In another embodiment of the invention the fastener is determined ashaving been tightened to its snug point when the angular displacement ofthe output means in response to one pulsed output is less than a firstreference predetermined forward angular displacement.

In a further embodiment of the invention the angular displacement of theoutput means from its snug point position is compared with a selectedone of a plurality of the second reference angular displacement aftereach pulsed output for determining when the fastener has been tightenedto the predetermined tightness.

Further the invention provides a method for tightening a fastener to apredetermined tightness using a pulsed output tightening tool having arotatable output means for tightening the fastener, the methodcomprising the steps of tightening the fastener to its snug point withthe rotatable output means, and monitoring the angular displacement ofthe output means from its angular position corresponding to the snugpoint of the fastener until the output means has rotated through asecond reference predetermined angular displacement from its snug pointposition corresponding to the predetermined tightness.

Therefore there is provided an impact wrench or other impulse tool fortightening a threaded fastener assembly to a significantly tightenedcondition of rotation, torque or yield. There is also provided a controlsystem using measurements of rotation and time for tightening a fastenerassembly to a clearly defined point such that there is extremely highprobability that the fastener has been tightened to the defined point.The invention also provides a self-contained control system mounted onan impact wrench that includes apparatus for measuring absolute shaftangular position, apparatus for receiving the angular position signalsand determining when the tightening process has started and for shuttingoff the tool when the fastener has reached a desired point ofsignificant tightness, and apparatus for generating electric power todrive the control system. The invention further provides an integral,self-contained impact wrench system that greatly improves the control offastener tightening and is robust, compact, inexpensive andself-contained.

The invention also provides a system for determining the snug orstarting point of the fastener tightening from the change in shaft speedas the starting point for angle tightening, as well as a system fordetermining the tightness of the fastener by measuring the forwardturning angle from the snug point. The invention provides a system inwhich the control algorithm stops the tightening process at a specificrotation angle and inspects the achieved torque and yield point, asystem with self-contained electrical power utilising the exhaust airfrom the tool to drive a small generator, as well as a system in whichthe start signal for each cycle is produced by the step voltage from thegenerator. The invention also provides a system in which the shut-offsignal for the tool is transmitted to a shut-off valve mounted off thetool by wire or wireless methods.

The advantages of the invention are many. A particularly importantadvantage achieved by the invention is that it facilitates relativelyaccurate tightening of a fastener to a desired predetermined tightness.This is achieved by virtue of the fact that the apparatus according tothe invention can relatively precisely determine the angulardisplacement of the output shaft of the pulsed output tightening tool inresponse to each pulsed tightening moment, and also by virtue of thefact that the apparatus according to the invention determines theabsolute angular position of the output shaft, which likewisecorresponds to the absolute angular position of the fastener. This,combined with the relatively accurate monitoring of the angulardisplacement of the shaft facilitates a determination of when thefastener is tightened to its snug point, and once the snug point isdetermined, then by relatively accurately determining the angulardisplacement of the output shaft from the snug point position, thetightness of the fastener can readily be determined, since the angulardisplacement of the output shaft from the snug point is proportional tothe torque to which the fastener is tightened.

These advantages of the invention are achieved largely by virtue of thefact that the detectable characteristic provided by the detectable meansalternates and smoothly cycles between a minimum value of the detectablecharacteristic and a maximum value of the detectable characteristic asthe output means rotates. By providing the detectable means as aneccentrically mounted member on the output shaft, and in particular, byproviding the detectable means as an eccentrically mounted member havinga cylindrical surface, a particular advantage of the invention isachieved by virtue of the fact that the cycling of the detectablecharacteristic between the respective minimum and maximum values isparticularly smooth, and thus provides an output of substantiallysinusoidal form. By detecting the detectable characteristic by a lightsensing means, a particularly advantageous form of the apparatusaccording to the invention is provided, in that the monitoring means isa contactless monitoring means, and thus robust. Indeed, by providingthe detectable means on the output means, a relatively accuratedetermination of the angular displacement of the fastener can bedetermined, since backlash is minimised, and furthermore, the apparatusaccording to the invention, and in turn a pulsed output tightening toolcomprising the apparatus according to the invention of relatively robustconstruction can be provided.

The invention will be more clearly understood from the followingdescription of a preferred embodiment thereof, which is given by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a partly cutaway, partly cross-sectional and partlydiagrammatic side elevational view of an impact wrench according to theinvention,

FIG. 2 is an end elevational view of a portion of the impact wrench ofFIG. 1,

FIG. 3 is a side elevational view of the portion of FIG. 2 of the impactwrench of FIG. 1,

FIG. 4 is a side elevational view of another portion of the impactwrench of FIG. 1,

FIG. 5 is a cross-sectional side elevational view of the portions ofFIGS. 2 to 4 assembled,

FIGS. 6(a) to (d) are cross-sectional end elevational views of theportion of FIG. 5 on the line VI—VI of FIG. 5,

FIG. 7 is a block representation of a monitoring and control circuit ofthe impact wrench of FIG. 1,

FIG. 8 is a graphical representation of signals of the impact wrench ofFIG. 1,

FIG. 9 is a graphical representation of absolute positions of an outputshaft of the impact wrench of FIG. 1, and

FIG. 10 is a look-up table of the impact wrench of FIG. 1.

Referring to the drawings, there is illustrated a pulsed outputtightening tool according to the invention which in this embodiment ofthe invention is an impact wrench indicated generally by the referencenumeral 1 for tightening a fastener (not shown), for example, a screw,nut or the like of a joint assembly (also not shown) to a predeterminedtightness. The impact wrench 1 comprises an outer casing 2 which definesa main body portion 3, and a handle 4 extending downwardly from the mainbody portion 3. An output means, namely, an output shaft 5 of circulartransverse cross-section is rotatably carried in a bearing 6 in the mainbody portion 3 of the casing 2 for outputting intermittent pulsedtightening moments for tightening, and also for loosening the fastener.The output shaft 5 defines a rotational axis 7 about which the outputshaft 5 is rotatable, and terminates at one end in a receiving means,namely, a square section receiver 8 for receiving a socket or otherappropriate fastener engaging element for engaging the fastener to betightened for loosened.

The output shaft 5 at its other end terminates in the main body portionin an anvil 9. A hammer mechanism 10, illustrated in blockrepresentation in FIG. 1, co-operates with the anvil 9 forintermittently impacting with the anvil 9, for in turn inducingintermittent pulsed tightening moments in the output shaft 5 forimparting to the fastener. A motor 11 which is also illustrated in blockrepresentation in FIG. 1, which in this embodiment of the invention is apneumatic motor, is located within the main body portion 3 for drivingthe hammer mechanism so that on each 360° of rotation of the motor shaftthe hammer mechanism 10 impacts with the anvil 9. A trigger switch 13 inthe handle 4 operates a pneumatic valve 14 also located in the handle 4for supplying pressurised air to the motor 11. These aspects of theimpact wrench 1 are substantially similar to a conventional impactwrench 1, and will be well known to those skilled in the art, as willthe operation of these aspects of the impact wrench 1, and inparticular, the operation of the hammer mechanism 10 of the impactwrench 1 will likewise be well known to those skilled in the art.Briefly, initially the output shaft 5 is continuously rotated by themotor 11 until the fastener meets resistance. Thereafter the hammermechanism 10 commences to operate and intermittently impacts with theanvil for intermittently outputting pulse tightening moments on theoutput shaft 5 to further tighten the fastener.

Air is supplied to the pneumatic valve 14 through a cut-out means,namely, a solenoid operated pneumatic cut-out valve 17 locatedexternally of but adjacent the handle 4 in an air supply line 18 to theimpact wrench 1. The cut-out valve 17 is responsive as will be describedbelow to the fastener being tightened to the predetermined tightness forcutting off the air supply to the motor 11. An inlet port 19 to thecut-out valve 17 is provided for connecting the cut-out valve 17 to thepressurised air supply.

Apparatus also according to the invention and indicated generally by thereference numeral 20 for determining when a fastener has been tightenedto the predetermined tightness is located within the main body portion 3around the output shaft 5 adjacent the anvil 9. The apparatus 20comprises a body member 21 which extends around the output shaft 5. Adetectable means, namely, an eccentrically disposed member 24 is locatedin the output shaft 5 within the body member 21 and provides a varyingdetectable characteristic as the output shaft 5 rotates, as will bedescribed below, for determining the absolute angular position of theoutput shaft 5, and also the angular displacement of the output shaft 5in response to each pulsed tightening moment outputted on the outputshaft 5. In this embodiment of the invention the eccentrically disposedmember 24 is integrally formed with the output shaft 5 during turning ofthe output shaft 5. However, it will be readily apparent to thoseskilled in the art that the eccentrically disposed member 24 could be abolt-on eccentrically disposed member which would facilitateretrofitting of the apparatus 20 to a conventional impact wrench. Theeccentrically disposed member 24 defines a cylindrical surface 25 and acentral axis 26 which extends parallel to but is offset from the mainrotational axis 7 of the output shaft 5. The diameter of theeccentrically disposed member 24 is less than the diameter of the outputshaft 5, and is selected along with the offset of the central axis 26from the main rotational axis 7 so that the cylindrical surface 25 ofthe eccentrically disposed member 24 is tangential to a cylindricalsurface 28 of the output shaft 5 at 29 adjacent the eccentricallydisposed member 24, see FIG. 4.

The body member 21 is of thickness t greater than the length I of theeccentrically disposed member 24, and is provided with a central bore 30of diameter just greater than the diameter of the cylindrical surface 28of the output shaft 5 for rotatably accommodating the output shaft 5 inthe body member 21. Additionally the body member 21 is located so thatthe eccentrically disposed member 24 is located completely within thecentral bore 30, see FIG. 5.

A pair of monitoring means for co-operating with the eccentricallydisposed member 24 for monitoring the absolute angular position of theoutput shaft 5, in this embodiment of the invention comprises a pair oflight sensing means provided by monitoring photo sensors 33 a and 33 b.The photo sensors 33 a and 33 b are located in corresponding lightaccommodating bores 34 a and 34 b which are disposed at 90° to eachother through the body member 21. The photo sensors 33 are located atone end 35 of the respective bores 34, and corresponding light sources,namely, light emitting diodes 36 a and 36 b are provided at the otherend 37 of the respective light accommodating bores 34 for directinglight through the respective bores 34 to the corresponding photo sensors33. The light accommodating bores 34 extend through and aresubstantially tangential to the central bore 30 through the body member21, which thus forms openings 38 at the respective areas of intersectionof the light accommodating bores 34 with the central bore 30. Theeccentrically disposed member 24 is accommodated into the respectivelight accommodating bores 34 as the output shaft 5 rotates.

The diameters and positioning of the light accommodating bores 34relative to the central bore 30 and the eccentrically disposed member 24is such that as the output shaft 5 rotates, the eccentrically disposedmember 24 extends into the respective light accommodating bores 34 foroccluding the respective light accommodating bores 34, and therebyrestricting the passage of light through the bores 34 to the photosensors 33. As the output shaft 5 rotates, the degree to which theeccentrically disposed member 24 occludes the respective lightaccommodating bores 34 alternates and smoothly cycles between maximumocclusion, whereby a minimum amount of light passes through the maximumoccluded light accommodating bore 34, and minimum occlusion, whereby amaximum amount of light passes through the minimum occluded lightaccommodating bore 34. For each 360° of rotation of the output shaft 5the amount of light passing through each bore 34 cycles between minimumand maximum. At maximum occlusion the eccentrically disposed member 24does not completely occlude the bores 34, but rather some light isallowed to pass through the bores 34 to the corresponding photo sensor33, see FIGS. 6(a) and 6(b) where the occlusion of the bores 34 a and 34b, respectively, is maximum. At minimum occlusion the eccentricallydisposed member 24 still partly occludes the bores 34, see FIGS. 6(c)and 6(d) where the occlusion of the bores 34 a and 34 b, respectively,is minimum.

Due to the fact that the surface 25 of the eccentrically disposed member24 is cylindrical, the eccentrically disposed member 24 transitionsprogressively and smoothly into the light accommodating bores 34 fromminimum to maximum occlusion, and transitions regressively and smoothlyfrom the light accommodating bores 34 from maximum to minimum occlusion.Thus, the level of light intensity received by the photo sensors 33transitions progressively and smoothly from minimum light intensity whenthe occlusion of the respective bores 34 is maximum to maximum lightintensity when the occlusion of the respective bores 34 by theeccentrically disposed member 24 is minimum, and vice versa. Thus, bysufficiently frequently reading the outputs of the photo sensors 33, aswill be described below, the angular displacement of the output shaft 5resulting from each pulsed tightening moment can be determined, and dueto the fact that a pair of photo sensors 33 are provided disposed aroundthe central bore 30 at 90° to each other, the absolute angular positionof the output shaft 5 can be determined.

In FIG. 6(a) the occlusion of the light accommodating bore 34 a by theeccentrically disposed member 24 is illustrated at a maximum. Also inFIG. 6(a) the light accommodating bore 34 b is approximately 50%occluded by the eccentrically disposed member 24. As the output shaft 5rotates in the direction of the arrow A, the degree of occlusion of thelight accommodating bore 34 a regresses, however, the degree ofocclusion of the light accommodating bore 34 b progressively increases.When the output shaft 5 has rotated through 90° from the angularposition illustrated in FIG. 6(a) to the position illustrated in FIG.6(b), the occlusion of the bore 34 b by the eccentrically disposedmember 24 is maximum, and the degree of occlusion of the lightaccommodating bore 34 a is approximately 50%. A further 90° rotation ofthe output shaft 5 in the direction of the arrow A to the positionillustrated in FIG. 6(c) leaves the light accommodating bore 34 a withminimum occlusion, and the light accommodating bore 34 b partly occludedwith approximately 50% occlusion, and so on. It should be noted herethat the edges 39 of the respective light accommodating bores 34 arealmost but not quite tangential to the eccentrically disposed member 24at minimum occlusion, so that at minimum occlusion the eccentricallydisposed member 24 projects slightly into the corresponding bore 34.

A control circuit 42, see FIG. 7, reads electronic output signals fromthe photo sensors 33 for determining the absolute angular position ofthe output shaft 5. However, before describing the control circuit 42 indetail, the signals outputted by the respective photo sensors 33 as theoutput shaft 5 rotates will first be described with reference to FIGS. 7and 8.

Referring now to FIG. 8, the output signals from the photo sensors 33are substantially similar, with the exception that since the photosensors 33 a and 33 b are angularly disposed at 90° to each other aroundthe output shaft 5 the output signals from the photo sensors 33 a and 33b are 90° out of phase with each other. FIG. 8 illustrates the signalsfrom the photo sensors 33 a and 33 b plotted against time for two 360°revolutions of the output shaft 5 when the output shaft 5 iscontinuously rotating at constant speed. The curve (a) represents theoutput from the photo sensor 33 a, and the curve (b) represents theoutput from the photo sensor 33 b. When the output shaft 5 iscontinuously rotating at constant speed, the output signals from thephoto sensors 33 are sinusoidal, and since they are 90° out of phasewith each other, one can be considered to be a sine wave, and the othera cosine wave in real time, as shown in FIG. 8.

FIG. 9 illustrates a plot of the absolute angular position of the outputshaft 5 against time which is computed by the monitoring and controlcircuit 42 from the output signals of the photo sensors 33 a and 33 b.During the period of time T₁ the output shaft 5 is running continuouslyat constant speed tightening the fastener. During the period of time T₁,approximately two and one half full cycles of the output shaft 5 areillustrated, namely, two and one half revolutions of the output shaft 5,each revolution being through 360°. The output shaft 5 is rotating at arelatively rapid speed of approximately 2,400 rpm, or one 360°revolution in each $\frac{1}{40}$second during the time period T₁. At the end of the time period T₁ atpoint A₁ of the curve, rotation of the output shaft 5 stops dead. Thiscould represent the angular position of the shaft corresponding to thesnug point of the fastener, or it could be an indication that the snugpoint of the fastener is being approached. On stopping dead at theangular position corresponding to the point Al, the output shaft 5bounces back due to backlash between the output shaft 5 and the fastenerbeing tightened. The point A₂ on the curve of FIG. 9 represents theabsolute angular position of the output shaft 5 after bounce-back. Oncethe output shaft 5 stops dead at the absolute angular positionrepresented by the point A₁ on the curve of FIG. 9, the impact wrenchoperates in the impact mode, and the hammer mechanism 10 imparts thefirst pulsed tightening moment on the output shaft 5, which urges theoutput shaft from the absolute position represented by the point A₂ tothe absolute angular position represented by the point A₃.

As can be seen in this case, the first pulsed tightening moment advancesthe output shaft 5 through a forward angular displacement ofapproximately 85°. The monitoring and control circuit 42 as will bedescribed below compares this angular displacement with a firstreference angular displacement which corresponds to the maximum angulardisplacement through which the output shaft 5 would rotate if the snugpoint had been reached. In this case, the angular displacement of 85° issignificantly in excess of the first reference angular displacement, andit is deemed that the snug point of the fastener had not been reached atthe point A₁. Due to backlash the output shaft 5 bounces back from theabsolute angular position represented by the point A₃ on the curve ofFIG. 9 to an absolute angular position represented by the point B, andthen settles at an absolute angular position represented by the point C.During the period between the point B and the point C while the nextpulsed tightening moment is awaited, noise can be seen on the curvebetween the point B and the point C. This noise may come from varioussources, but is insignificant and does not affect the operation of themonitoring and control circuit 42. The point C represents the absoluteangular position of the output shaft 5 when the next pulsed tighteningmoment is applied on the output shaft 5. The pulsed tightening momentadvances the output shaft 5 through an angular displacement to anabsolute angular position represented by the point D on the curve ofFIG. 9. The angular displacement between the points C and D isapproximately 10°, and is deemed to be less than the first referenceangular displacement. Thus, the fastener is deemed to have beentightened to its snug point when the output shaft 5 was at the absoluteangular position represented by the point C on the curve of FIG. 9.

The monitoring and control circuit 42 monitors the angular displacementof the output shaft 5 from the absolute angular position represented bythe point C until the output shaft 5 has rotated through a secondreference angular displacement, at which stage the fastener is deemed tohave been tightened to the desired degree of tightness. In this case,after the point D the output shaft 5 bounces back to an angular positionrepresented by the point F on the curve 9. Between the points D and Fnoise which is insignificant is experienced. The next pulsed tighteningmoment advances the output shaft 5 from an absolute angular positionrepresented by the point F to an angular position represented by thepoint G. Further bounce-back and noise is experienced and the outputshaft 5 settles at an absolute angular position represented by the pointH. The next two pulsed tightening moments advance the output shaft 5through further angular displacement to respective absolute angularpositions represented by the points I and J. At the absolute angularposition represented by the point J, the monitoring and control circuit42 determines that the absolute angular displacement of the output shaft5 from the snug point represented by the point C is equal to or greaterthan the second reference angular displacement, and the fastener 5 isdeemed to be tightened to the predetermined tightness.

Since the output shaft 5 is continuously engaged with the fastener, theangular displacement of the output shaft 5 for each pulsed tighteningmoment is similar to the angular displacement of the fastener allowingfor backlash which may result from a loose fitting socket or fastenerengaging element engaged on the fastener. However, any discrepancyresulting from backlash between the angular rotation of the fastener andthe output shaft 5 is taken account of provided that the angulardisplacement is measured from the points A₂, C, E, F, H, etc. of thecurve of FIG. 9 in response to the corresponding next pulsed tighteningmoment rather than from the points A₁, A₃, D, G, etc., therebyeliminating the effect of backlash.

The value of the second reference angular displacement will varydepending on the joint, the fastener being tightened, and in particular,on the diameter, thread size and material of the fastener, and typicallywill lie in the range of 30° to 120° and, in general, in the range of30° to 90°. The value of the first reference angular displacement, ingeneral, will be a fixed value of approximately 20°, although provisionmay be made for selectively altering it.

It is known that once the snug point of a fastener has been reached, theangular displacement of the fastener from its snug point is proportionalto the tightness of the fastener, and therefore indirectly to the torqueapplied. Thus, by determining the total forward angular displacement ofthe output shaft in the direction in which the pulsed tightening momentsare being applied from the snug point position a determination as towhen the fastener is tightened to the predetermined tightness can bemade.

Referring now to FIG. 7, the monitoring and control circuit 42 will nowbe described. The monitoring and control circuit 42 is powered by arechargeable battery 45. A pneumatically powered electrical generator 47is located in the handle 4 of the input wrench 1 through which exhaustair from the pneumatic motor 11 is exhausted. The exhaust air operatesthe generator 47 for charging the battery 45, and also for providing astart signal on the line 48 for commencing operation of the circuit 42.The output signals from the photo sensors 33 a and 33 b are voltagesignals, the voltage of which is proportional to the intensity of thelight received, and thus, inversely proportional to the degree ofocclusion of the corresponding bores 34. The output signals aredelivered to the circuit 42 on lines 49 a and 49 b, respectively. Thecircuit 42 comprises a calibration circuit 50 for calibrating the impactwrench 1 each time on start-up as will be described below. A powersupply switch 52 which is located in the handle 4, but not illustratedin FIG. 1 powers the circuit 42 from the battery 45. A calibrationinitiating circuit 54 initiates calibration in response to the powerswitch 52. A timer circuit 53 co-operates with the calibration circuit50 for calibration of the impact wrench 1.

A computing means, namely, a computing circuit 55 comprises a firstblock 56 which continuously determines the absolute angular position ofthe output shaft 5 from signals received from the photo sensors 33 a and33 b. A second block 57 determines when the fastener has been tightenedto its snug point, and a third block 58 determines when the output shaft5 has been rotated through an angular displacement from its snug pointposition corresponding to the second reference angular displacement fordetermining when the fastener has been tightened to the predeterminedtightness.

An input circuit 59 facilitates inputting of the second referenceangular displacements. The first reference angular displacement ispre-programmed and stored in the second block 58. A stop circuit 60 inresponse to the third block 58 determining that the fastener has beentightened to the predetermined tightness outputs a signal to the cut-outvalve 17 for isolating the impact wrench 1 from the pneumatic supply,thereby terminating tightening of the fastener. A visual display 62 isprovided for displaying an indication to a user that calibration of theimpact wrench 1 is being carried out, and for indicating completion ofcalibration. The visual display 62 also displays the angulardisplacement of the output shaft 5 resulting from each pulsed tighteningmoment. The visual display 62 also indicates when the fastener has beentightened to the predetermined tightness, and indicates when the impactwrench 1 is reset and ready for the next fastener to be tightened.

Initially the impact wrench 1 is connected to the pneumatic supply, andthe power switch 52 is closed, thus supplying the circuit 42 with powerfrom the battery 45. The closing of the power switch 52 activates thecalibration initiating circuit 54 which sets the calibration circuit 50to be ready to commence calibration. The impact wrench 1 is calibratedby running the impact wrench 1 in a no load state, in other words,disconnected from a fastener, and in the no load state the output shaft5 runs continuously at constant speed. Once the generator 47 commencesto generate power, the power output signal on the line 48 activates thecalibration circuit 50 to commence calibration.

The calibration circuit 50 reads the signals from the first and secondsensors 33 a and 33 b on the lines 49 a and 49 b. At predetermined timeintervals the signals are read, and a look-up table is compiled whichcorrelates the voltage values of the voltage output signals of thesensors 33 a and 33 b against absolute angular positions of the outputshaft 5. A typical look-up table is illustrated in FIG. 10. The outputvoltage values of the sensor 33 a are set out in column 1, while theoutput voltage values of the sensor 33 b are set out in column 2. Thecorresponding angular value of the output shaft 5 is set out in column3. While for convenience the look-up table shows the angle incrementsbeing 6°, in practice reading of the output signals of the sensors 33 aand 33 b will be taken at sufficiently frequent intervals so that theangle increments will be approximately 1.5°.

Once the look-up table has been compiled, calibration is completed, anda signal is sent to the computing circuit 55 indicating that calibrationhas been completed and the impact wrench 1 is ready for normaloperation. The calibration circuit 50 outputs a signal to the visualdisplay 62 during calibration to select a display indicating thatcalibration is in progress, and on calibration being completed a furthersignal is outputted by the calibration circuit 50 to the visual display62 for indicating completion of calibration. The calibration circuitalso outputs a signal on the completion of calibration to the stopcircuit 60 which trips the cut-out valve 17 to isolate the impact wrenchfrom the pneumatic supply, thus also indicating termination ofcalibration.

An operator then wishing to tighten a fastener inputs the secondreference angular displacements through the input 59, and connects theimpact wrench 1 to the fastener by, for example, a socket or othersuitable element, and on depressing the trigger 14 air is supplied fromthe pneumatic supply to the motor 11. The output signal from thegenerator 47 on the line 48 activates the first block 56 for determiningthe absolute angular position of the output shaft 5. The first block 56reads the output signals from the sensors 33 a and 33 b and from thelook-up table of FIG. 10 continuously determines the absolute angularposition of the output shaft 5.

When continuous rotation of the output shaft 5 ceases, the impact wrench1 commences to output pulsed tightening moments in response to thehammer mechanism 10. On continuous rotation of the output shaft 5ceasing, the absolute angular position of the shaft 5 is stored by thesecond block 57. After the first pulsed tightening moment has beenoutputted on the output shaft 5, the absolute angular position of theoutput shaft 5 is again determined, and the second block 57 determinesif the angular displacement of the output shaft 5 from the previousangular position is less than the first reference angular displacement,and if so, the block 57 determines that the previous absolute angularposition of the output shaft 5 is the snug point position. Otherwise,the impact wrench continues to output pulsed tightening moments untilthe block 57 determines that the angular displacement of the outputshaft resulting from the last pulsed tightening moment is less than thefirst reference angular displacement, thus indicating that the previousabsolute angular position of the shaft is the snug point position whichcorresponds to the snug point of the fastener. On the snug pointposition being determined, the absolute angular position of the snugpoint of the shaft is stored in the third block 58, which then reads thecumulative angular displacements of the output shaft 5 resulting fromeach pulsed tightening moment until the output shaft 5 has beendisplaced through the second reference angular displacement from thesnug point position. On the third block 58 determining that the outputshaft has rotated through the second reference angular displacement fromthe snug point position, the fastener is deemed to be tightened to thepredetermined tightness, and the block 58 outputs a signal to the stopcircuit, which in turn outputs a signal to the cut-out valve 17 forisolating the impact wrench 1 from the pneumatic supply, therebyterminating tightening of the fastener.

In this embodiment of the invention two selector switches (not shown)are provided for facilitating inputting of the first and secondreference angular displacements.

Each selector switch is a multi-selector switch, thus allowing for oneof a number of first and second reference angular displacements to beselected and inputted.

In use, the impact wrench 1 is operated as already described. Initially,the impact wrench 1 is operated with no load on the output shaft 5,which is run continuously at constant speed to facilitate calibration.On completion of calibration the output wrench 1 is connected to thefastener to be tightened, and tightening of the fastener proceeds asalready described.

Each time the cut-out solenoid valve 17 isolates the impact wrench 1from the pneumatic supply, the cut-out valve 17 is reset automatically.

While the detectable means has been described as being provided by aneccentrically disposed member, other suitable detectable means may beused. For example, the detectable means could provide a detectablecharacteristic, which could, for example, be a magnetic characteristic,and by monitoring the magnetic field generated by the detectable meansas the output shaft rotated, a determination of the angular displacementand the absolute position of the output shaft could be made. Needless tosay, other suitable detectable means which provide a detectablecharacteristic could be used. Indeed, it will be appreciated thatinstead of determining the angular displacement of the output shaft andits absolute position by monitoring the position of the eccentricallydisposed member using light sensing means, other suitable sensing meansmay be provided, for example, a proximity sensor, an inductive sensor, amagnetic or other optical sensors.

Additionally, it will be appreciated that where the detectable meansprovides a detectable magnetic field, it will be appreciated that thedetectable member need not be provided by an eccentrically disposedmember, indeed, a magnet located in the output shaft eccentricallyrelative to the rotational axis of the output shaft would be sufficient.

While the impact wrench has been described as being pneumaticallypowered, the impact wrench may be powered by any other suitable means,for example, the impact wrench may be powered by an hydraulic powersupply through an hydraulic motor, or by an electrically powered motor.

Additionally, while the apparatus for determining when a fastener istightened to a predetermined tightness has been described as beingincorporated in an impact wrench, the apparatus may be incorporated inany other type of pulsed output tightening tool. Additionally, while theeccentrically disposed member has been described as being integrallyformed with the output shaft, it will be appreciated that the apparatusaccording to the invention for determining when a fastener is tightenedto a predetermined tightness could be supplied separately from theimpact wrench to be retrofitted to existing impact wrenches. Indeed, itis envisaged that the apparatus according to the invention fordetermining when a fastener is tightened to a predetermined degree oftightness could be retrofitted externally of the impact wrench on theoutput shaft by mounting the apparatus on the receiver at the end of theoutput shaft, and providing a receiver extending from the apparatus forreceiving a socket or other suitable fastener engaging element. In whichcase, the apparatus could be anchored to the casing of the impactwrench, and the monitoring circuitry could be provided in a separatecasing associated with the apparatus 20.

It is also envisaged that the cut-out valve 17 may be located within theimpact wrench housing, and indeed, where the cut-out valve 17 is locatedexternally of the housing of the impact wrench, it may be locatedremotely of the impact wrench, and in which case it is envisaged that aradio transmitter may be provided in the stop circuit for transmitting astop signal to a receiver adjacent the cut-out valve 17 which would tripthe cut-out valve.

1. Apparatus for use in a pulsed output tightening tool for determiningwhen fastener being tightened by a rotatable output means of the tool istightened to a predetermined tightness, the apparatus comprising adetectable means for mounting on the rotatable output means of the tooland being rotatable therewith for providing a detectable characteristicas the output means rotates about its rotational axis, and a monitoringmeans for monitoring the detectable means for determining rotationalangular displacement of the output means, characterized in that thedetectable means provides the detectable characteristic as acharacteristic which alternately and smoothly cycles between a minimumvalue and a maximum value as the output means rotates, and a pair ofmonitor means are disposed at angularly spaced apart locations aroundthe detectable means operating with the detectable means for outputtingsignals indicative of the absolute angular position of the output means,for facilitating a determination of the angular displacement of theoutput means in response to each pulsed output of the output means fordetermining when the fastener is tightened to the predeterminedtightness.
 2. Apparatus as claimed in claim 1 characterized in that therespective monitoring means are disposed at 90° to each other around thedetectable means.
 3. Apparatus as claimed in claim 1 characterized inthat the detectable characteristic of the detectable means cyclesthrough each of the minimum and maximum values of the detectablecharacteristic at least once for each 360° angular displacement of theoutput means.
 4. Apparatus as claimed in claim 1 characterized in thateach monitoring means outputs an electronic signal, and the monitoringmeans cooperate with each other for detecting the absolute angularposition of the output means.
 5. Apparatus as claimed in claim 1characterized in that a means is provided for determining when thefastener is tightened to its snug point.
 6. Apparatus as claimed inclaim 5 characterized in that the means for determining when thefastener is tightened to its snug point is responsive to the monitoringmeans detecting the first stalling of the output means after tighteningof the fastener commences.
 7. Apparatus as claimed in claim 5characterized in that the means for determining when the fastener istightened to its snug point is responsive to the monitoring meansdetecting the angular displacement of the output means being less than afirst reference predetermined angular displacement in response to onepulsed output of the output means.
 8. Apparatus as claimed in claim 5characterized in that the means for determining when the fastener istightened to the predetermined tightness is responsive to the monitoringmeans determining that the rotatable output means has rotated a secondreference predetermined angular displacement from its snug pointposition.
 9. Apparatus as claimed in claim 1 characterized in that thedetectable means comprises an eccentrically disposed membereccentrically disposed relative to the output means, the eccentricallydisposed member defining a central axis, and being adapted for mountingon the output means with the central axis of the eccentrically disposedmember spaced apart from and parallel to the rotational axis of theoutput means for causing the eccentrically dispose member to rotateeccentrically with the output means.
 10. Apparatus as claimed in claim 1characterized in that each monitoring comprises a light sensing means,each light sensing means cooperating with the detectable means so thatlight passing the detectable means to the light sensing means is atleast partially occluded by the detectable means as the output meansrotates, and the degree of occlusion alternates between minimum andmaximum values corresponding to the minimum and maximum values of thedetectable characteristic.
 11. Apparatus as claimed in claim 7characterized in that a body member is provided adjacent the detectablemeans, and a pair of light accomodating bores extend through the bodymember for directing light onto the corresponding light sensing means,an opening being provided into each light accomodating bore foraccomodating the detectable means into the light accomodating bores asthe output means rotates so that each light accomodating bore is atleast partly occluded by the detectable means as the output meansrotates, the degree of occlusion alternating between the respectiveminimum and maximum values thereof as the output means rotates. 12.Apparatus as claimed in claim 11 characterized in that a light source isprovided at one end of each light accomodating bore and thecorresponding light sensing means is provided at the other end thereof,the openings for accomodating the detectable means into the respectivelight accomodating bores being located intermediate the ends thereof.13. Apparatus as claimed in claim 11 characterized in that at maximumocclusion the detectable means substantially occludes the correspondinglight accomodating bore.
 14. Apparatus as claimed in claim 1characterized in that the apparatus comprises a calibrating means forcalibrating the apparatus, the calibrating means being operable forcalibrating the apparatus when the output means is rotating at asubstantially constant speed.
 15. A pulsed output tightening toolcomprising an output means rotatably mounted about a rotational axis forintermittently imparting a pulsed tightening moment to a fastener fortightening thereof, a detectable means being mounted on the output meansand being rotatable therewith for providing a varying detectablecharacteristic as the output means rotates, and a monitoring means formonitoring the detectable means for determining rotational angulardisplacement of the output means characterized in that the detectablemeans provides the detectable characteristic as a characteristic whichalternately and smoothly cycles between a minimum value and a maximumvalue as the output means rotates, and a pair of monitoring means aredisposed at angularly spaced apart locations around the detectable meanscooperating with the detectable means for outputting signals indicativeof the absolute angular position of the output means, for facilitating adetermination of the angular displacement of the output means inresponse to each pulsed output of the output means for determining whenthe fastener is tightened to the predetermined tightness.
 16. A pulsedoutput tightening tool as claimed in claim 15 characterized in that therespective monitoring means are disposed at 90° to each other around thedetectable means.
 17. A pulsed output tightening tool as claimed inclaim 15 characterized in that the detectable characteristic of thedetectable means cycles through each of the minimum and maximum valuesof the detectable characteristic at least once for each 360° angulardisplacement of the output means.
 18. A pulsed output tightening tool asclaimed in claim 15 characterized in that each monitoring means outputsan electronic signal, and the monitoring means cooperate with each otherfor detecting the absolute angular position of the output means.
 19. Apulsed output tightening tool as claimed in claim 15 characterized inthat a means is provided for determining when the fastener is tightenedto its snug point.
 20. A pulsed output tightening tool as claimed inclaim 19 characterized in that the means for determining when thefastener is tightened to its snug point is responsive to the monitoringmeans detecting the first stalling of the output means after tighteningof the fastener commences.
 21. A pulsed output tightening tool asclaimed in claim 19 characterized in that the means for determining whenthe fastener is tightened to its snug point is responsive to themonitoring means detecting the angular displacement of the output meansin response to a pulsed output being less than a first referencepredetermined angular displacement.
 22. A pulsed output tightening toolas claimed in claim 19 characterized in that the means for determiningwhen the fastener is tightened to the predetermined tightness isresponsive to the monitoring means determining that the rotatable outputmeans has rotated a second reference predetermined angular displacementfrom its snug point position.
 23. A pulsed output tightening tool asclaimed in claim 15 characterized in that the detectable means comprisesan eccentrically disposed member eccentrically disposed relative to theoutput means, the eccentrically disposed member defining a central axis,and being mounted on the output means with the central axis of theeccentrically disposed member spaced apart from and parallel to therotational axis of the output means for causing the eccentricallydisposed member to rotate eccentrically with the output means.
 24. Apulsed output tightening tool as claimed in claim 15 characterized inthat each monitoring means comprises a light sensing means, each lightsensing means cooperating with the detectable means so that lightpassing the detectable means to the light sensing means is at leastpartially occluded by the detectable means as the output means rotates,and the degree of occlusion alternates between minimum and maximumvalues corresponding to the minimum and maximum values of the detectablecharacteristic.
 25. A pulsed output tightening tool as claimed in claim17 characterized in that a body member is provided adjacent thedetectable means, and a pair of light accomodating bores extend throughthe body member for directing light onto the corresponding light sensingmeans, an opening being provided into each light accomodating bore foraccomdating the detectable means into the light accomodating bores asthe output means rotates so that each light accomodating bore is atleast partly occluded by the detectable means as the output meansrotates, the degree of occlusion alternating between the respectiveminimum and maximum values thereof as the output means rotates.
 26. Apulsed output tightening tool as claimed in claim 25 characterized inthat at maximum occlusion the detectable means substantially occludesthe corresponding light accomodating bore, and at minimum occlusion thedetectable means just slightly occludes the corresponding lightaccomodating bore.
 27. A pulsed output tightening tool as claimed inclaim 25 characterized in that a light source is provided at one end ofeach light accomodating bore and the corresponding light sensing meansis provided at the other end thereof, the openings for accomodating thedetectable means into the respective light accomodating bores beinglocated intermediate the the ends thereof.
 28. A pulsed outputtightening tool as claimed in claim 15 characterized in that the pulsedoutput tightening tool is an impact wrench, and the output shaft extendsfrom an anvil, a hammer mechanism being provided for cooperating withthe anvil for intermittently impacting with the anvil for providing therespective pulsed tightening moments, a drive means comprising apneumatic motor being provided for operating the hammer mechanism forintermittently impacting with the anvil, and a pneumatic turbineelectrical generator being located adjacent an exhaust from thepneumatic motor for recovering power from the exhaust of the pneumaticmotor for generating electricity for powering the monitoring means. 29.A method for determining when a fastener is tightened to a predeterminedtightness by a rotatable output means of a pulsed output tighteningtool, the method comprising the steps of locating a detectable means onthe rotatable output means of the tool to be rotatable with the outputmeans for providing a varying detectablee characteristic as the outputmeans rotates about its rotational axis, and providing a monitoringmeans for monitoring the detectable means for determining rotationalangular displacement of the output means, characterized in that thedetectable means provides the detectable characteristic as acharacteristic which alternately and smoothly cycles between a minimumvalue and a maximum value as the output means rotates, and a pair ofmonitoring means are disposed at angularly spaced apart locations aroundthe detectable means and cooperated with the detectable means foroutputting signals indicative of the absolute angular position of theoutput means for facilitating a determination of the angulardisplacement of the output means in response to each pulsed output ofthe output means for determining when the fastener is tightened to thepredetermined tightness.
 30. A method as claimed in claim 22characterized in that the respective monitoring means are disposed at90° to each other around the detectable means.
 31. A method as claimedin claim 29 characterized in that the detectable characteristic of thedetectable means cycles through each of the minimum and maximum valuesof the detectable characteristic at least once for each 360° angulardisplacement of the output means.
 32. A method as claimed in claim 29characterized in that the method further comprises determining when thefastener is tightened to its snug point, the snug point being determinedin response to the monitoring means detecting the first stalling of theoutput means after tightening of the fastener commences, and thefastener is determined as being tightened to the predetermined tightnesswhen the output means has rotated a second reference predeterminedangular displacement from the snug point position.